Motor Problem

[Kentucky 250x]

I Just purchased a 87 250x at a local Bike shop. The owner of the shop said he just replaced rings (Stock bore), 2 Valves. You can tell from looking that there is a new head gasket and cylinder gasket. Any way today was the first chance i was able to get out and ride it. Had been riding for about an hour and i heard a noise like a nail was stuck in a tire and deflated. Really quick. The motor died. i went to kick it and there was not any compression. Any thoughts on what it may be. I dont know if the Shop is going to stand behind it. :

[Aceman]

If you just bought it take it back to the shop and have them look at it. It sounds like either you dropped a valve or a valve is stuck open. If you dropped a valve though it would of made quite a bit of knocking when it cut out.